Notes: Occurs on a large sandstone boulder outcrop in sycamore-oak riparian habitat of Atascadero Creek on the side of Highway 41 West.

Thallus white, 5cm diameter, with some crystals on lobes, especially tips, no hairs on lobe margins, lobe margin up to 2.5mm, but usually smaller, K+Y, medulla white, K-, lower side white with whitish to dark simple rhizines. No soredia or isidia present, apothecia 1-2(4)mm, disc black with distinct white pruina.

In the Nash key, you need to accept that the pruina on the lobes constitutes “crystals”. It seems light on this specimen, but if you go the other way you end up at Physcia halei, which does not have pruina on the apothecia disc, among other minor differences.

Comments

Crystals were much more distinct on a recent observation of P. biziana on oak bark, so this one I had to make sure I understood if it fit within the “crystal” definition. I think I got my bearings now…